1) Field of the Invention
The present invention relates generally to agricultural implements and, more specifically, to a spring trip standard for tillage implements.
2) Related Art
Spring trip standards typically include a mounting bracket attached to rectangular toolbar and extending upwardly and rearwardly to a downwardly and forwardly directed spring abutment surface. A spring is compressed between the abutment surface and an upwardly directed spring abutment surface on a support member pivotally connected to the lower portion of the bracket. A tool-supporting shank is fixed to the member. As the tool encounters obstacles, the support member and shank pivot upwardly against the bias of the spring so the tool can move over the obstacle. The angle of the lower spring abutment surface relative to the spring centerline changes as the support member pivots upwardly. The change in angle introduces spring buckling forces and causes the spring to curve so the lowermost spring coil is maintained against the spring abutment surface. The buckling action reduces the effectiveness of the spring and can result in premature spring breakage.
To reduce shank assembly complexity and reduce manufacturing time and costs, some spring trip standards include integral stops so that a tension link extending through the coils of the spring is obviated. One such standard is shown and described in our copending U.S. patent application Ser. No. 09/216,270, filed Dec. 18, 1998 and entitled SPRING TRIP STANDARD. The tension link provided a built-in spring guidance feature to help reduce excessive spring buckling, and therefore standards without such links, such as shown in our above-referenced application, are more prone to have spring buckling problems.
In some spring trip shank assemblies, such as shown in U.S. Pat. No. 4,520,878, the bottom of the coil spring rests on a seat which can swivel to maintain the lower face of the spring substantially normal to the longitudinal axis of the spring and thereby reduce spring buckling forces. In another type of assembly shown in U.S. Pat. No. 3,700,039, the lower end of the coil spring is free to rock on a clamp bolt to remain normal to the centerline of the spring. Such arrangements require numerous components and are relatively difficult to assemble. The swiveling seat construction and the bolt support arrangement introduce additional wear components into the assembly.